Which begs the question...are the banks recognizing them, or distributing them?
Do they respond to the "normal" counterfeit detection methods?
For people who handle a lot of cash money (like tellers) yes they usually spot them. The special marking pens do NOT spot them which is what so many small businesses use.
They have since made arrests in LA involving illegals and smugglers, but when the bills were circulating, we kept a real hundred for comparison.
The two things I remember most is that the fakes were to slick even for a crisp new bill as they had a coating to prevent the pens from detecting them and one serial number was backwards, making it readable from the backside of the bill instead of the from the bill face.
Most people could not detect the slickness unless they had a better than average sense of touch. I work with fibers professionally so I spotted that right off. The serial number was definitely the best and most obvious tip off.